With marked growth of atomic energy industry, radiation shielding in atomic energy facilities has become of significant importance in recent years. In fields such as analytical chemistry and medical treatment, radiation has also been increasingly utilized. Thus it has been desired to develop a radiation-shielding material and a radiation-sensitive material. In particular, a highly radiation-sensitive material has been desired not only for the protection of operators from the danger of exposure to radiation, but also in fields such as chemical and structural analyses utilizing radiation, and measurement of integrated intensity of radiation.
Heretofore, a radiation-sensitive material comprising a sheet-shaped mold with a composition containing a fluorescent pigment emitting light upon irradiation with radiation (e.g., calcium tungstate and silver-activated zinc sulfide) coated on the surface thereof has been used. These fluorescent pigments, however, are of low sensitivity and can sense only a large dose of radiation. Moreover, such conventional fluorescent pigments give rise to problems such as generation of secondary radiation. Thus the conventional radiation-sensitive material is not sufficiently useful as a material for sensing a small dose of radiation. In particular, in view of safety problems such as shielding of radiation and environmental pollution as well as the generation of secondary radiation, the fluorescent pigments are limited in their use.
Japanese Patent Application (OPI) No. 133349/81 (the term "OPI" as used herein means a "published unexamined Japanese patent application") discloses a scintillation converter for neutron radiography which is produced by molding a composition composed of polyethylene, an inorganic boron compound, and a zinc sulfide-base fluorescent material. This scintillation converter for neutron radiography, however, has several disadvantages because polyethylene is used as a polymeric material. For example, when the composition is molded into a sheet, for example, shrinkage occurs, and when the sheet is bonded to a metallic plate (e.g., an aluminum plate), it is bent. Thus, when the state or structure of the inside of a test specimen is examined, measured and photographed after irradiation with neutron radiation, an accurate image cannot be obtained. In extending the plate surface by press molding at a temperature at which the polyethylene becomes molten, it is necessary to increase the pressing pressure, and, furthermore, the area can be extended only to a small extent. Thus a scintillation converter having a large surface area is difficult to produce. Moreover, since the molten tension drops, it is necessary to raise the press temperature; this leads to brown coloration of the zinc sulfide and a reduction in fluorescent performance.